1filter

: a device that is used to remove something unwanted from a liquid or gas that passes through it

: a device that prevents some kinds of light, sound, electronic noises, etc., from passing through

computers : software that prevents someone from looking at or receiving particular kinds of material through the Internet

Full Definition of FILTER

1

a: a porous article or mass (as of paper or sand) through which a gas or liquid is passed to separate out matter in suspension

b: an apparatus containing a filter medium

2

a: a device or material for suppressing or minimizing waves or oscillations of certain frequencies (as of electricity, light, or sound)

b: a transparent material (as colored glass) that absorbs light of certain wavelengths or colors selectively and is used for modifying light that reaches a sensitized photographic material —called also color filter

3

: something that has the effect of a filter (as by holding back elements or modifying the appearance of something) <his work is too often viewed through the filter of race — Brent Staples>